1. Field of the Invention
This invention relates to an improved water based aerosol marking paint. More specifically, it relates to a water based aerosol marking paint having a high non-volatile content suitable for marking on asphalt or dirt. In addition, this invention uses a straight chain, low molecular weight hydrocarbon to control surface foaming. The invention provides an excellent water based paint for applications in which water based aerosol paints have not previously been suitable.
2. Description of the Prior Art
Water based spray paint formulations have been available for some time. The advantages of incorporating water into an aerosol paint formulation are well known: reduction of flammability and cost, as well as a reduction of volatile organic compounds that may be hazardous or contribute to air pollution. These paints typically include a water reducible resin for forming the paint film, water, a water miscible solvent, a water compatible propellant such as dimethyl ether or similar compounds, and pigments. See, for example, Brouillette et al. (U.S. Pat. No. 4,518,734); Rapaport et al. U.S. Pat. No. 4,482,662); Rapaport et al. (U.S. Pat. No. 4,420,575); Page et al. (U.S. Pat. No. 4,384,661); Suk (U.S. Pat. No. 4,450,253); and Suk (U.S. Pat. No. 4,265,797).
The water borne aerosol coatings disclosed in the prior art have been used exclusively for decorative spray coatings that typically provide a convenient means for touching up small areas or objects. They have not been suitable for carrying the high non-volatile content necessary for site marking purposes. Paints used for site marking (typically on porous and uneven surfaces such as asphalt or dirt) must provide an opaque, high visibility, long-lasting mark to assure a positive communication of site data to others who are working in the same area.
Prior art emulsified or water reducible aerosol coatings have also exhibited a marked tendency to produce surface foam in the applied film. This problem is characteristic of all oil-in-water aerosol formulations, and results from entrapped volatile hydrophobic propellant escaping from the continuous high surface tension water film. Brouillette et al. claim to have solved this problem by using dimethyl ether as a propellant. However, in practice the foaming problem has continued. The prior art teaches various methods to deal with this foaming problem using different defoamer compounds, which are generally based on silicone derivatives. These compounds are relatively expensive and only partially remedy the foaming problem.